Mover and linear motor

ABSTRACT

A mover, in which at each outer surface of a cornered tubular inner yoke, a flat plate magnet magnetized from inside to outside in a direction perpendicular to the outer surface, a flat plate magnet magnetized in an axial direction of the inner yoke, a flat plate magnet magnetized from outside to inside in the direction perpendicular to the outer surface, and a flat plate magnet magnetized in the axial direction of the inner yoke are alternately provided in this order, is passed through an armature in which a first single pole unit and a second single pole unit rotated by 90° with respect to the first single pole unit are alternately stacked, thus forming a linear motor. Windings are collectively wound around core portions of the first single pole unit. Positions of the magnets provided at the outer surfaces of the inner yoke are deviated from each other.

This application is the national phase under 35 U. S. C. §371 of PCTInternational Application No. PCT/JP2010/050761 which has anInternational filing date of Jan. 22, 2010 and designated the UnitedStates of America.

BACKGROUND

1. Technical Field

The present invention relates to a mover provided with a plurality offlat plate permanent magnets at outer surfaces of a cornered tubularinner yoke, and to a linear motor formed by a combination of the moverand an armature (stator).

2. Description of Related Art

In a vertical movement device of a drill used in a borer for anelectronic circuit board or the like or a vertical movement mechanism ina robot of a pick-and-place type (which picks a component and places thecomponent at a predetermined position), for example, high-speed movementand high-precision positioning are required. Accordingly, suchrequirements cannot be satisfied by a conventional method for convertingan output of a rotation motor into a parallel motion (vertical motion)using a ball screw because the movement speed is low in the conventionalmethod.

Therefore, for such a vertical movement, the use of a linear motorcapable of directly deriving a parallel motion output is being promoted.Various types of structures have been proposed for a linear motor inwhich a rectangular permanent magnet structure provided with a largenumber of plate-like permanent magnets is used as a mover, an armaturehaving a winding to flow the current is used as a stator, and the moveris arranged in the portion of hole of the stator (see Japanese PatentApplication Laid-Open No. 2002-359962 and Japanese Patent ApplicationLaid-Open No. 2008-228545, for example).

SUMMARY

In a conventional linear motor, response is quick as compared with thecase where a ball screw is used, but since the mass of a mover is large,it is impossible to realize a response speed at a required level eventhough it is possible to ensure sufficient thrust force. A structure ofa linear motor suitable for speed enhancement is a movable magnet typestructure; however, when a magnetic pole pitch is large, the amount ofmagnetic flux traveling around to reach an inner yoke on a back surfaceof a magnet is increased, and the volume of the inner yoke is increased,thus increasing the weight of the mover. On the other hand, when themagnetic pole pitch is reduced, a winding structure in an armature iscomplicated, which makes it difficult to realize a linear motor havingsmaller size and higher output. Furthermore, a linear motor isinfluenced by its own weight when it is used for a vertical movement;hence, weight reduction is increasingly desired, and in addition, highrigidity is required for a mover in order to realize a high-speedoperation.

The present invention has been made in view of the above-describedcircumstances, and its object is to provide a mover having a largeamount of generated magnetic flux, reduced weight, and high rigidity.

Another object of the present invention is to provide a mover thatreduces thrust ripple and enables a smooth movement.

Still another object of the present invention to provide a linear motorhaving a structure in which magnetic saturation is unlikely to occur,and capable of realizing high-speed responsiveness and enhancingconversion efficiency of the motor to realize a high power density.

Still yet another object of the present invention is to provide a linearmotor in which reduction in thrust ripple and/or detent force isenabled, a smooth movement is allowed, and improvement in positionaccuracy is also promoted.

Even yet another object of the present invention is to provide atwo-phase drive linear motor that enables a smooth movement of a mover,which is substantially similar to that of a mover of a three-phase drivelinear motor.

A mover according to the present invention is a mover of a linear motor,which is provided with a plurality of flat plate permanent magnets atouter surfaces of a cornered tubular inner yoke made of a soft magneticmaterial, wherein the plurality of flat plate permanent magnets includeflat plate magnets magnetized in a direction perpendicular to the outersurface of the inner yoke and flat plate magnets magnetized in an axialdirection of the inner yoke, and the flat plate magnets magnetized inthe perpendicular direction and the flat plate magnets magnetized in theaxial direction are alternately and continuously arranged at each outersurface of the inner yoke along the axial direction of the inner yoke,wherein the flat plate magnets magnetized in the perpendicular directioninclude first flat plate magnets magnetized from inside of the inneryoke to outside thereof and second flat plate magnets magnetized fromthe outside of the inner yoke to the inside thereof, and the first andsecond flat plate magnets are alternately arranged along the axialdirection of the inner yoke, wherein the flat plate magnets magnetizedin the axial direction are each magnetized from the adjacent second flatplate magnet to the adjacent first flat plate magnet, and whereinpositions of the plurality of flat plate permanent magnets provided atthe outer surfaces of the inner yoke are deviated from each other.

In the mover of the present invention, at each outer surface of thecornered tubular inner yoke made of a soft magnetic material, the flatplate magnet magnetized from inside to outside in the directionperpendicular to the outer surface, the flat plate magnet magnetized inthe axial direction of the inner yoke, the flat plate magnet magnetizedfrom outside to inside in the direction perpendicular to the outersurface, and the flat plate magnet magnetized in the axial direction ofthe inner yoke are arranged in this order along the axial direction ofthe inner yoke, and the positions of the flat plate magnets provided atthe outer surfaces of the inner yoke are deviated from each other.Accordingly, since the flat plate magnets magnetized in the axialdirection are each provided between the two flat plate magnetsmagnetized in the direction perpendicular to the outer surface, magneticflux generated in the inner yoke located inside the mover is reduced,thus making it possible to reduce the thickness of the inner yoke and toreduce the resulting weight. Further, since the flat plate magnets canbe provided at the respective outer surfaces of the inner yoke in adivided manner, fabrication flexibility is extremely high as comparedwith a cylindrical mover, and the use of high-performance magnets isalso enabled, thereby increasing rigidity. Furthermore, since thepositions of the magnets provided at the outer surfaces are deviatedfrom each other in the axial direction (movement direction), thrustripple and/or detent force are/is reduced, and cogging is suppressed,thus enabling a smooth movement.

In the mover according to the present invention, the positions of theplurality of flat plate permanent magnets provided at the outer surfacesof the inner yoke are deviated from each other in the axial direction bya dimension equal to or less than ¼ of a total length of one of thefirst flat plate magnets, one of the second flat plate magnets and twoof the flat plate magnets magnetized in the axial direction.

In the mover of the present invention, the positions of the plurality offlat plate magnets provided at the outer surfaces, i.e., a field cycleof a set of four flat plate magnets, are displaced (deviated) by adimension equal to or less than ¼ of the above length. When no deviationis made, large thrust ripple is generated to make it difficult to enablea smooth movement, which might adversely affect accurate positioning.However, when a field cycle of a set of four flat plate magnets isdeviated by a dimension greater than ¼ of the above length, both ofsouth and north poles of the magnets of the mover might face the samearmature magnetic poles, and the south and north poles might be invertedto make it impossible to obtain sufficient thrust force. Hence, thefield cycle is displaced (deviated) by a dimension equal to or less than¼ of the above length, thus reducing thrust ripple and realizing asmooth linear movement.

Note that in the mover of the present invention, the flat plate magnetsmagnetized in the axial direction of the inner yoke may be removed fromthe above-described structure. Specifically, in such a variation, ateach outer surface of a cornered tubular inner yoke made of a softmagnetic material, first flat plate magnets magnetized from inside tooutside in a direction perpendicular to the outer surface and secondflat plate magnets magnetized from outside to inside in the directionperpendicular to the outer surface are alternately arranged along anaxial direction of the inner yoke, and positions of the flat platemagnets provided at the outer surfaces of the inner yoke are deviatedfrom each other. For example, the positions of the flat plate magnetsprovided at the outer surfaces of the inner yoke are deviated from eachother in the axial direction by a dimension equal to or less than ¼ of atotal length of one of the first flat plate magnets and one of thesecond flat plate magnets. This variation also achieves effects similarto those achieved in the example of the foregoing structure providedwith a plurality of sets of the flat plate magnets in which each setincludes four flat plate magnets.

A mover according to the present invention is a mover of a linear motor,which is provided with a plurality of flat plate permanent magnets atfour outer surfaces of a quadrangular tubular inner yoke made of a softmagnetic material, wherein the plurality of flat plate permanent magnetsinclude flat plate magnets magnetized in a direction perpendicular tothe outer surface of the inner yoke and flat plate magnets magnetized inan axial direction of the inner yoke, and the flat plate magnetsmagnetized in the perpendicular direction and the flat plate magnetsmagnetized in the axial direction are alternately and continuouslyarranged at each outer surface of the inner yoke along the axialdirection of the inner yoke, wherein the flat plate magnets magnetizedin the perpendicular direction include first flat plate magnetsmagnetized from inside of the inner yoke to outside thereof and secondflat plate magnets magnetized from the outside of the inner yoke to theinside thereof, and the first and second flat plate magnets arealternately arranged along the axial direction of the inner yoke,wherein the flat plate magnets magnetized in the axial direction areeach magnetized from the adjacent second flat plate magnet to theadjacent first flat plate magnet, and wherein positions of the pluralityof flat plate permanent magnets provided at one pair of the adjacentouter surfaces of the inner yoke and positions of the plurality of flatplate permanent magnets provided at the other pair of the adjacent outersurfaces of the inner yoke are deviated from each other by ¼ of a totallength of one of the first flat plate magnets, one of the second flatplate magnets and two of the flat plate magnets magnetized in the axialdirection.

In the mover of the present invention, at each outer surface of thequadrangular tubular inner yoke made of a soft magnetic material, thefirst flat plate magnet magnetized from inside to outside in thedirection perpendicular to the outer surface, the flat plate magnetmagnetized in the axial direction of the inner yoke, the second flatplate magnet magnetized from outside to inside in the directionperpendicular to the outer surface, and the flat plate magnet magnetizedin the axial direction of the inner yoke are arranged in this orderalong the axial direction of the inner yoke, and the positions of theplurality of flat plate magnets provided at one pair of the adjacentouter surfaces of the inner yoke (i.e., the magnets opposed to one ofwindings of an armature) and the positions of the plurality of flatplate magnets provided at the other pair of the adjacent outer surfacesof the inner yoke (i.e., the magnets opposed to the other winding of thearmature) are deviated from each other by ¼ of a total length of one ofthe first flat plate magnets, one of the second flat plate magnets andtwo of the flat plate magnets magnetized in the axial direction (i.e.,by an electrical angle of 90°). Hence, drive currents by which a phasedifference of 90° occurs are passed through the respective windings ofthe armature, thereby continuously generating thrust force for the moverand realizing a smooth movement by two-phase drive.

In the mover according to the present invention, a linear guide rail forsupporting the mover is provided at a corner portion of the outersurface of the inner yoke so as to be extended in the axial direction ofthe inner yoke.

In the mover of the present invention, the linear guide rail is providedat the corner portion of the outer surface of the inner yoke so as to beextended in the axial direction thereof, thus supporting the mover.Hence, the mover is pressed laterally through the linear guide rail,thereby making it possible to suppress vibrations such as flexuralvibration and resonant vibration and to realize a high-speed linearmovement in which no oscillation occurs.

A linear motor according to the present invention includes: a mover inwhich a plurality of flat plate permanent magnets at outer surfaces of acornered tubular inner yoke made of a soft magnetic material includeflat plate magnets magnetized in a direction perpendicular to the outersurface of the inner yoke and flat plate magnets magnetized in an axialdirection of the inner yoke, the flat plate magnets magnetized in theperpendicular direction and the flat plate magnets magnetized in theaxial direction are alternately and continuously arranged at each outersurface of the inner yoke along the axial direction of the inner yoke,the flat plate magnets magnetized in the perpendicular direction includefirst flat plate magnets magnetized from inside of the inner yoke tooutside thereof and second flat plate magnets magnetized from theoutside of the inner yoke to the inside thereof, the first and secondflat plate magnets are alternately arranged along the axial direction ofthe inner yoke, the flat plate magnets magnetized in the axial directionare each magnetized from the adjacent second flat plate magnet to theadjacent first flat plate magnet, and positions of the plurality of flatplate permanent magnets provided at the outer surfaces of the inner yokeare deviated from each other; and an armature in which the armatureincludes a first single pole unit made of a soft magnetic material andhaving a rectangular opening, a yoke portion located outwardly of theopening, and a core portion extended from the yoke portion to theopening, and a second single pole unit made of a soft magnetic materialand having a rectangular opening, a yoke portion located outwardly ofthe opening, and a core portion that is located at a position rotated by90° from a position of the core portion of the first single pole unitand that is extended from the yoke portion to the opening, the first andsecond single pole units are alternately stacked, and windings are woundaround a plurality of the core portions of the first single pole unitand/or a plurality of the core portions of the second single pole unit,wherein the mover is passed through the opening of the first single poleunit and the opening of the second single pole unit.

A linear motor according to the present invention includes: a mover inwhich a plurality of flat plate permanent magnets at outer surfaces of acornered tubular inner yoke made of a soft magnetic material includefirst flat plate magnets magnetized from inside of the inner yoke tooutside thereof and second flat plate magnets magnetized from theoutside of the inner yoke to the inside thereof, the first and secondflat plate magnets are alternately arranged at each outer surface of theinner yoke along the axial direction of the inner yoke, and positions ofthe plurality of flat plate permanent magnets provided at the outersurfaces of the inner yoke are deviated from each other; and an armaturein which the armature includes a first single pole unit made of a softmagnetic material and having a rectangular opening, a yoke portionlocated outwardly of the opening, and a core portion extended from theyoke portion to the opening, and a second single pole unit made of asoft magnetic material and having a rectangular opening, a yoke portionlocated outwardly of the opening, and a core portion that is located ata position rotated by 90° from a position of the core portion of thefirst single pole unit and that is extended from the yoke portion to theopening, the first and second single pole units are alternately stacked,and windings are wound around a plurality of the core portions of thefirst single pole unit and/or a plurality of the core portions of thesecond single pole unit, wherein the mover is passed through the openingof the first single pole unit and the opening of the second single poleunit.

The linear motor of the present invention is formed so that theforegoing mover is passed through the armature in which the first singlepole unit made of a soft magnetic material and having the rectangularopening, the yoke portion located outwardly of the opening, and the coreportion extended from the yoke portion to the opening, and the secondsingle pole unit made of a soft magnetic material and having a structurerotated by 90° from that of the first single pole unit are alternatelystacked, and the windings are collectively wound around the coreportions of one of the single pole units. Since a reduction in weight ofthe mover is enabled, a response speed of the mover is increased.Further, a winding structure in the armature is simple, thus enablingsize reduction. Furthermore, since the positions of the magnets providedat the outer surfaces of the mover are deviated in the axial direction(_(movement direction), thrust ripple and/or detent force are/is reduced, thus enabling a high-speed and stable movement of the mover.)

A linear motor according to the present invention includes: a mover inwhich a plurality of flat plate permanent magnets at four outer surfacesof a quadrangular tubular inner yoke made of a soft magnetic materialinclude flat plate magnets magnetized in a direction perpendicular tothe outer surface of the inner yoke and flat plate magnets magnetized inan axial direction of the inner yoke, the flat plate magnets magnetizedin the perpendicular direction and the flat plate magnets magnetized inthe axial direction are alternately and continuously arranged at eachouter surface of the inner yoke along the axial direction of the inneryoke, the flat plate magnets magnetized in the perpendicular directioninclude first flat plate magnets magnetized from inside of the inneryoke to outside thereof and second flat plate magnets magnetized fromthe outside of the inner yoke to the inside thereof, the first andsecond flat plate magnets are alternately arranged along the axialdirection of the inner yoke, the flat plate magnets magnetized in theaxial direction are each magnetized from the adjacent second flat platemagnet to the adjacent first flat plate magnet, and positions of theplurality of flat plate permanent magnets provided at one pair of theadjacent outer surfaces of the inner yoke and positions of the pluralityof flat plate permanent magnets provided at the other pair of theadjacent outer surfaces of the inner yoke are deviated from each otherby ¼ of a total length of one of the first flat plate magnets, one ofthe second flat plate magnets and two of the flat plate magnetsmagnetized in the axial direction; and an armature in which the armatureincludes a first single pole unit made of a soft magnetic material andhaving a rectangular opening, a yoke portion located outwardly of theopening, and a core portion extended from the yoke portion to theopening, and a second single pole unit made of a soft magnetic materialand having a rectangular opening, a yoke portion located outwardly ofthe opening, and a core portion that is located at a position rotated by90° from a position of the core portion of the first single pole unitand that is extended from the yoke portion to the opening, the first andsecond single pole units are alternately stacked, and first and secondwindings are wound around two areas of a plurality of the core portionsof the first single pole unit or a plurality of the core portions of thesecond single pole unit, wherein the mover is passed through the openingof the first single pole unit and the opening of the second single poleunit so that the plurality of flat plate permanent magnets at said onepair of the outer surfaces are opposed to the first winding and theplurality of flat plate permanent magnets at the other pair of the outersurfaces are opposed to the second winding, and wherein currents bywhich a phase difference of an electrical angle of 90° occurs areapplied to the first and second windings.

In the linear motor of the present invention, the positions of the flatplate magnets provided in the mover and opposed to one of the windingsof the armature, and the positions of the flat plate magnets provided inthe mover and opposed to the other winding of the armature are deviatedfrom each other by ¼ of a field cycle (i.e., by an electrical angle of90°). Hence, drive currents (e.g., sinusoidal wave current and cosinewave current) by which a phase deviation of 90° occurs are passedthrough the respective windings of the armature, thereby continuouslygenerating thrust force for the mover by a single core unit, andenabling a smooth movement by two-phase drive.

In the linear motor according to the present invention, the positions ofthe plurality of flat plate permanent magnets provided at said one pairof the outer surfaces are deviated from each other, and the positions ofthe plurality of flat plate permanent magnets provided at the other pairof the outer surfaces are deviated from each other.

In the linear motor of the present invention, while the relationship ofdeviation between the positions of the flat plate magnets provided so asto be opposed to one of the windings and the positions of the flat platemagnets provided so as to be opposed to the other winding is maintained,the positions of the flat plate magnets provided at one pair of theouter surfaces are deviated from each other, and the positions of theflat plate magnets provided at the other pair of the outer surfaces aredeviated from each other, thus reducing harmonic components of thrustripple and detent force in a two-phase drive system.

In the linear motor according to the present invention, spacing betweenthe first and second single pole units, which are adjacent to eachother, is adjusted.

In the linear motor of the present invention, the spacing between thefirst and second single pole units of the armature (i.e., spacingbetween magnetic pole teeth) is adjusted, thereby reducing harmoniccomponents of thrust ripple and detent force in a two-phase drivesystem.

In the linear motor according to the present invention, the inner yokehas a quadrangular tubular shape, the openings each have a quadrangularshape, the first and second single pole units each have a quadrangularshape, and an angle of 45° is formed between a direction of a side ofeach of the first and second single pole units and a direction of a sideof the opening.

In the linear motor of the present invention, the mover having aquadrangular tubular shape is passed through the quadrangular openingsof the quadrangular first and second single pole units of the armature,and the directions of the sides of the openings are inclined by 45° withrespect to the directions of the sides of the first and second singlepole units. Hence, the flow of magnetic flux through the armature issmoothed, thus making it difficult to cause magnetic saturation.Moreover, effective formation of the core portions is enabled even whenthe shape of the armature is reduced in size.

In the linear motor according to the present invention, a spacer made ofa soft magnetic material is interposed between the stacked first andsecond single pole units so that the core portions of the first andsecond single pole units do not come into contact with each other.

In the linear motor of the present invention, the spacer having aframe-like shape is provided between the first and second single poleunits. Hence, prevention of contact between the core portions of thefirst single pole unit and the core portions of the second single poleunit (i.e., avoidance of magnetic short circuit) is realized with asimple structure. Besides, the spacing between the first and secondsingle pole units is easily adjustable.

In a magnet row A having a cyclic magnetic flux density distribution,assume that a cyclic direction is an x direction and a magnetic fluxdensity at a position x is B(x) (where B(x)=(B(x)_(x), B(x)_(y),B(x)_(z))). Then, 2τ(2τ=λ) by which B(x)=B(x+2τ) is defined as a fieldcycle (where τ represents a magnetic pole pitch).

Furthermore, in magnet rows A₁ and A₂ each having a cyclic magnetic fluxdensity distribution, assume that a cyclic direction is an x direction,a magnetic flux density of A₁ at a position x is B₁(x), and a magneticflux density of A₂ at the position x is B₂(x). Then, a magnetic fluxdensity distribution B₂ 40 provided when the magnet row A₂, for example,is moved by d in the x direction in a magnetic row arrangement in whichB₁(x)=B₁(x+2τ₁), B₂(x)=B₂(x+2τ₂), and τ1=τ2 is represented as follows:B₂′=B₂(x-d) where d is defined as a deviation. In this case, −λ/4<d<λ/4,and −τ/2<d<τ/2.

In the present invention, a reduction in magnetic flux generated in theinner yoke inside the mover is enabled, thus making it possible toreduce the thickness of the inner yoke and to reduce the weight of theresulting linear motor. Further, since the magnets can be provided atthe outer surfaces of the inner yoke in a divided manner, selectivity ofusable magnets is improved, thus enabling enhancement of rigidity of themover. Hence, implementation of a high-speed linear motor is enabled.Furthermore, since the positions of the flat plate magnets provided atthe outer surfaces are deviated from each other in the axial direction(movement direction), reduction in thrust ripple and/or detent force isenabled, thus making it possible to realize a smooth movement of themover and to implement the linear motor with improved positionalaccuracy.

Besides, in the present invention, the mover is formed so that thearrangement of the flat plate magnets at one pair of the adjacent outersurfaces of the quadrangular tubular inner yoke (i.e., at the twosurfaces opposed to one of the windings of the armature) and thearrangement of the flat plate magnets at the other pair of the adjacentouter surfaces of the inner yoke (i.e., at the two surfaces opposed tothe other winding of the armature) are deviated from each other by ¼ ofa length of one set of the flat plate magnets (i.e., by λ/4 where λdenotes a field cycle, or by an electrical angle of 90°), and currentsby which a phase difference of 90° occurs are passed through one of thewindings and the other winding in the armature, thus making it possibleto realize a movement of the mover by two-phase drive and to provide thelinear motor, the length of which is shorter than that of a three-phasedrive linear motor.

Moreover, in the present invention, the arrangements of the flat platemagnets at one pair of the outer surfaces and at the other pair of theouter surfaces and/or the spacing between magnetic pole teeth in thearmature are/is adjusted, thereby making it possible to solve a problem(e.g., large thrust ripple and detent force) in a two-phase drive linearmotor and to realize a smooth movement substantially similar to that ofa three-phase drive linear motor.

The above and further objects and features will more fully be apparentfrom the following detailed description with accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a structure of a moveraccording to a first embodiment.

FIG. 2A is a perspective view illustrating a structure of an armatureused for a linear motor.

FIG. 2B is a perspective view illustrating a structure of the armatureused for a linear motor.

FIG. 2C is a perspective view illustrating a structure of the armatureused for a linear motor.

FIG. 3A is a perspective view illustrating a structure of the armatureused for a linear motor.

FIG. 3B is a perspective view illustrating a structure of the armatureused for a linear motor.

FIG. 4 is a perspective view illustrating a structure of a linear motoraccording to the first embodiment.

FIG. 5 is a partially broken perspective view illustrating the structureof the linear motor according to the first embodiment.

FIG. 6 is a cross-sectional view illustrating a flow of the current andmagnetomotive force in an armature.

FIG. 7 is a perspective view illustrating a structure of a moveraccording to a second embodiment.

FIG. 8A is a perspective view illustrating a structure of an armatureaccording to the second embodiment.

FIG. 8B is a perspective view illustrating a structure of the armatureaccording to the second embodiment.

FIG. 8C is a perspective view illustrating a structure of the armatureaccording to the second embodiment.

FIG. 9 is a perspective view illustrating a structure of a linear motoraccording to the second embodiment.

FIG. 10 is a perspective view illustrating a structure of a moveraccording to a third embodiment.

FIG. 11 is a perspective view illustrating a structure of a moveraccording to a fourth embodiment.

FIG. 12 is a perspective view illustrating a structure of a linear motoraccording to the fourth embodiment.

FIG. 13 is a partially broken perspective view illustrating thestructure of the linear motor according to the fourth embodiment.

FIG. 14 is a cross-sectional view of a standard armature.

FIG. 15 is a cross-sectional view of an armature for describing a methodfor reducing second-order and sixth-order harmonic components.

FIG. 16 is a perspective view of a mover for describing a method forreducing a fourth-order harmonic component.

FIG. 17 is a cross-sectional view of an armature for describing a methodfor reducing an eighth-order harmonic component.

FIG. 18A is a plan view illustrating an armature material used forfabrication of the armature according to the first embodiment.

FIG. 18B is a plan view illustrating an armature material used forfabrication of the armature according to the first embodiment.

FIG. 19 is a graph illustrating results of measurement of thrustcharacteristics in the linear motor according to the first embodiment.

FIG. 20A is a top view illustrating a state in which the mover accordingto the fourth embodiment is passed through the armature.

FIG. 20B is a side view illustrating the state in which the moveraccording to the fourth embodiment is passed through the armature.

FIG. 20C is a cross-sectional view illustrating the state in which themover according to the fourth embodiment is passed through the armature.

FIG. 21A is a plane view illustrating an armature material used forfabrication of the armature according to the fourth embodiment.

FIG. 21B is a plane view illustrating an armature material used forfabrication of the armature according to the fourth embodiment.

FIG. 22 is a cross-sectional view illustrating a core unit provided by afirst harmonic component reduction method.

FIG. 23 is a graph illustrating results of measurement of thrustcharacteristics in the linear motor according to the fourth embodiment.

FIG. 24 is a cross-sectional view illustrating a core unit provided by asecond harmonic component reduction method.

FIG. 25 is a cross-sectional view illustrating a core unit provided by athird harmonic component reduction method.

FIG. 26 is a graph illustrating results of measurement of thrustcharacteristics in a linear motor according to a fifth embodiment.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described based on thedrawings illustrating embodiments thereof.

First Embodiment

FIG. 1 is a perspective view illustrating a structure of a moveraccording to a first embodiment of the present invention. A mover 1 isformed so that four types of flat plate magnets 3 a, 3 b, 3 c and 3 dare alternately provided in this order at each outer surface of aquadrangular tubular inner yoke 2, made of a soft magnetic material,along an axial direction of the inner yoke 2 (i.e., along a movementdirection of the mover 1). In FIG. 1, open arrows indicate magnetizationdirections of the respective flat plate magnets 3 a, 3 b, 3 c and 3 d.Each flat plate magnet (first flat plate magnet) 3 a is a flat platepermanent magnet magnetized from inside to outside in a directionperpendicular to the outer surface of the inner yoke 2. On the otherhand, each flat plate magnet (second flat plate magnet) 3 c is a flatplate permanent magnet magnetized from outside to inside in a directionperpendicular to the outer surface of the inner yoke 2. Hence, themagnetization directions of the flat plate magnets 3 a and 3 c areperpendicular to the outer surface of the inner yoke 2 and are oppositeto each other.

Further, the flat plate magnets 3 b and 3 d are flat plate permanentmagnets each magnetized from the adjacent flat plate magnet 3 c to theadjacent flat plate magnet 3 a along the axial direction of the inneryoke 2 (i.e., along a longitudinal direction of the outer surfacethereof). Hence, the magnetization directions of the flat plate magnets3 b and 3 d correspond to the axial direction of the inner yoke 2 andare opposite to each other.

Furthermore, positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the outer surfaces of the inner yoke 2 are deviated fromeach other by a dimension equal to or less than ¼ of a total length ofone set of the four types of the flat plate magnets 3 a, 3 b, 3 c and 3d. In the example illustrated in FIG. 1, at the four outer surfaces ofthe quadrangular tubular inner yoke 2, the positions of the flat platemagnets 3 a, 3 b, 3 c and 3 d provided at the two opposing outersurfaces coincide with each other, but the positions of the flat platemagnets 3 a, 3 b, 3 c and 3 d provided at the two adjacent outersurfaces are deviated by a length of the flat plate magnet 3 b or 3 d.

FIGS. 2A to 2C and FIGS. 3A and 3B are perspective views eachillustrating a structure of an armature used for a linear motoraccording to the present invention, and FIGS. 2A to 2C and FIG. 3A arepartial schematic diagrams thereof while FIG. 3B is an overall schematicdiagram thereof.

An armature 4 is formed so that a quadrangular plate first single poleunit 5 illustrated in FIG. 2A and a quadrangular plate second singlepole unit 6 illustrated in FIG. 2B are alternately arranged, and aframe-like spacer unit 11 such as one illustrated in FIG. 2C is insertedbetween the first and second single pole units 5 and 6 adjacent to eachother (see FIG. 3A).

The first single pole unit 5 is made of a soft magnetic material andhas: a quadrangular opening 5 a through which the mover 1 passes; a yokeportion 5 b serving as a frame body located outwardly of the opening 5a; and a core portion 5 c extended from the yoke portion 5 b toward theopening 5 a. An angle of 45° is formed between the direction of a sideof the quadrangular plate first single pole unit 5 and that of a side ofthe opening 5 a. Further, the second single pole unit 6 is made of asoft magnetic material and has: a quadrangular opening 6 a through whichthe mover 1 passes; a yoke portion 6 b serving as a frame body locatedoutwardly of the opening 6 a; and a core portion 6 c extended from theyoke portion 6 b toward the opening 6 a. An angle of 45° is formedbetween the direction of a side of the quadrangular plate second singlepole unit 6 and that of a side of the opening 6 a. The second singlepole unit 6 has a structure rotated by 90° from that of the first singlepole unit 5.

The spacer unit 11 made of a soft magnetic material and consisting onlyof yokes is inserted between the first and second single pole units 5and 6 adjacent to each other, thus preventing the core portions of thesingle pole units 5 and 6 from coming into contact with each other.Further, a single-phase unit such as one illustrated in FIG. 3A isformed by alternately arranging and stacking the above-described firstsingle pole unit 5, second single pole unit 6 and spacer unit 11 in thefollowing order: the first single pole unit 5, the spacer unit 11, thesecond single pole unit 6, the spacer unit 11, . . . . In thesingle-phase unit, the yoke portions 5 b and 6 b of the first and secondsingle pole units 5 and 6 adjacent to each other are brought intocontact with each other, but the core portions 5 c and 6 c thereof arenot brought into contact with each other, so that a gap existstherebetween, thus avoiding magnetic short circuit.

A winding 8 a is collectively wound around the core portions 5 c (eachcorresponding to the upper core portion 5 c in FIG. 2A) of the firstsingle pole units 5 so as to be passed through gap portions 7 a and 7 bcommon to the first and second single pole units 5 and 6; in addition, awinding 8 b is collectively wound around the other core portions 5 c(each corresponding to the lower core portion 5 c in FIG. 2A) of thefirst single pole units 5 so as to be passed through gap portions 7 cand 7 d common to the first and second single pole units 5 and 6.Furthermore, the windings 8 a and 8 b are connected so that energizationdirections of the windings 8 a and 8 b are opposite to each other (seeFIG. 3B).

Moreover, the foregoing mover 1 illustrated in FIG. 1 is passed througha hollow portion 9 formed by the continuous openings 5 a and 6 a of thearmature 4 illustrated in FIG. 3B, thus forming a single-phase drivelinear motor (single-phase unit) 10 according to the first embodiment.FIG. 4 is a perspective view illustrating a structure of the linearmotor 10 according to the present invention, and FIG. 5 is a partiallybroken perspective view illustrating the structure of the linear motor10.

In such a linear motor, the armature 4 functions as a stator. Further,currents are passed through the windings 8 a and 8 b in oppositedirections, thus causing a reciprocating linear motion of the mover 1,passed through the hollow portion 9 of the armature 4, with respect tothe armature 4 (stator).

FIG. 6 is a cross-sectional view illustrating a flow of the current andmagnetomotive force in the armature 4. In FIG. 6, “• (direction ofapplied current from the rear of the plane to the front thereof)” and “x(direction of applied current from the front of the plane to the rearthereof” indicate directions of current to the windings 8 a and 8 b, andopen arrows indicate directions of magnetomotive force applied to thecore portions 5 c and 6 c due to coil energization. By passing currentsthrough the windings 8 a and 8 b in opposite directions, magnetic fieldsare generated in all the core portions 5 c and 6 c of the first andsecond single pole units 5 and 6.

Note that in the foregoing example, the spacer unit 11 having aframe-like shape and consisting only of yokes is inserted between thesingle pole units adjacent to each other; thus, even when the singlepole units have a uniform thickness as a whole, the core portions of thesingle pole units are prevented from coming into contact with eachother. According to this example, for each single pole unit, thethickness of the core portion does not have to be smaller than that ofthe yoke portion and thus no additional process is necessary, so thatthe use of the single pole units having a uniform thickness as a wholeis enabled, thereby simplifying a fabrication process.

On the other hand, the single pole units may be formed so that thethickness of the core portion is made smaller than that of the yokeportion in each single pole unit and the core portions of the singlepole units do not come into contact with each other when the resultingsingle pole units are stacked. In such an example, the foregoing spacerunit 11 is unnecessary.

For a conventional cylindrical linear motor, a structure in which aradially magnetized cylindrical magnet is adhered to a solid inner yokeor a structure in which an axially magnetized cylindrical magnet isadhered to a solid inner yoke, for example, has been used. In such astructure, the inner yoke is large and the mass of a mover is increased,thus making it difficult to achieve a high-speed responsiveness. On theother hand, in the mover 1 described above, the inner yoke 2 is hollow;furthermore, a reduction in magnetic flux generated inside the inneryoke 2 is enabled, and a reduction in thickness of the cornered tubularinner yoke 2 is enabled, thus enabling a reduction in weight of themover 1. Hence, an increase in the response speed of the mover 1 isenabled.

Further, examples of methods for reducing the thickness of an inner yokeof a mover include a method for reducing a magnet pole pitch; however,when a pole pitch is reduced, the number of areas where windings arelocated is increased in a structure of a conventional armature, and theresulting shape tends to increase in size. On the other hand, in thearmature 4, a winding is not wound for each pole but the windings 8 aand 8 b are collectively wound; therefore, even when a magnetic polepitch is small, a winding structure is not complicated but is simplyprovided, thus facilitating size reduction.

Furthermore, since the mover 1 has a rectangular cross-sectional shape(quadrangular cross-sectional shape in the foregoing example) in thelinear motor 10, magnets can be provided at a plurality of surfaces(four surfaces in the foregoing example) in a divided manner, and inaddition, the use of flat plate magnets is enabled. Hence, as comparedwith a cylindrical linear motor, fabrication flexibility, includingselection of magnets to be used, is extremely high, and the fabricationof the mover 1 having high rigidity can be easily carried out.

Moreover, the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the adjacent outer surfaces of the inner yoke 2 of the mover1 are deviated from each other in the axial direction of the inner yoke2 (i.e., in the movement direction of the mover 1). Hence, the effect ofreducing thrust ripple and/or detent force can be achieved, therebymaking it possible to eliminate cogging and to realize a smooth linearmovement of the mover 1.

In addition, the directions of sides of the openings 5 a and 6 a of thesingle pole units 5 and 6 are inclined by 45° with respect to thedirections of sides of main bodies of the first and second single poleunits 5 and 6. Hence, the flow of magnetic flux through the armature 4is smoothed, thus making it difficult to cause magnetic saturation.

Note that although five sets of the flat plate magnets 3 a, 3 b, 3 c and3 d, i.e., a total of twenty flat plate magnets, are providedsequentially in a continuous manner at each outer surface of the inneryoke 2 in the foregoing embodiment, such a structure is provided by wayof example, and the number of the flat plate magnets may be any number.Further, although two sets of the first and second single pole units 5and 6 are alternately arranged, this arrangement is provided by way ofexample, and the number of sets may be any number.

Furthermore, although the shape of the inner yoke 2 is a quadrangulartubular shape in the foregoing embodiment, this shape is provided by wayof example, and the inner yoke 2 may have a different polygonal tubularshape such as an octagonal tubular shape.

Besides, although the windings 8 a and 8 b are collectively wound aroundthe core portions 5 c of the first single pole units 5 in the foregoingembodiment, windings may be collectively wound around the core portions6 c of the second single pole units 6.

In the foregoing embodiment, at the four outer surfaces of thequadrangular tubular inner yoke 2, the positions of the flat platemagnets 3 a, 3 b, 3 c and 3 d provided at the two opposing outersurfaces coincide with each other, and the positions of the flat platemagnets 3 a, 3 b, 3 c and 3 d provided at the two adjacent outersurfaces are deviated from each other. However, the positions of theflat plate magnets 3 a, 3 b, 3 c and 3 d provided at the four outersurfaces of the inner yoke 2 may be slightly deviated from each other sothat all the positions are different. It is to be noted that even insuch a structure example, a maximum deviation amount is equal to or lessthan ¼ of a length of one set of the four flat plate magnets 3 a, 3 b, 3c and 3 d.

The single-phase linear motor (single-phase unit) has been describedthus far; however, for example, when a three-phase drive linear motor isformed, three of the foregoing armatures may be provided linearly atintervals in accordance with the following expression: magnetic polepitch×(n+⅓) or magnetic pole pitch×(n+⅔) where n is an integer, and themover may be passed through these armatures. Note that in such a case,the integer n may be set in consideration of space in which windings arecontained.

Second Embodiment

FIG. 7, FIGS. 8A to 8C and FIG. 9 are perspective views illustratingstructures of a mover 21, an armature 4 and a linear motor 30 accordingto the second embodiment, respectively. In FIG. 7, FIGS. 8A to 8C andFIG. 9, the same components as those in FIG. 1, FIGS. 2A to 2C and FIGS.3A and 3B are identified by the same reference numerals, and thedescription thereof will be omitted.

In the mover 21 illustrated in FIG. 7, linear guide rails 12 areprovided at two corner portions of outer surfaces of an inner yoke 2 soas to be extended axially. Moreover, cut-outs for allowing the linearguide rails 12 to pass through openings of first and second single poleunits 5 and 6 constituting the armature 4 may be provided. At front andrear surfaces of a main body illustrated in FIG. 8A in which the foursingle pole units are stacked, mover support frames 14 illustrated inFIG. 8B and equipped with linear guide sliders 13 are provided, thusforming the armature 4 of a single-phase unit (see FIG. 8C). Further,the mover 21 illustrated in FIG. 7 is passed through the armature 4illustrated in FIG. 8C, thus forming the single-phase drive linear motor(single-phase unit) 30 (see FIG. 9).

In the second embodiment, the mover 21 is supported by being pressedlaterally through the linear guide rails 12. Hence, further enhancementin rigidity is enabled. Furthermore, vibrations such as flexuralvibration and resonant vibration can be suppressed by the linear guiderails 12. Accordingly, even when a high-speed movement is made, no largevibration occurs, thus making it possible to realize a stable high-speedlinear movement in which no oscillation occurs.

Third Embodiment

A third embodiment is a variation of the first embodiment describedabove. FIG. 10 is a perspective view illustrating a structure of a moveraccording to the third embodiment. A mover 31 according to the thirdembodiment has a structure in which the flat plate magnets 3 b and 3 dmagnetized in the axial direction are removed from the mover 1 (seeFIG. 1) according to the first embodiment. Specifically, the mover 31 isformed so that at each outer surface of the quadrangular tubular inneryoke 2 made of a soft magnetic material, the two types of the flat platemagnets 3 a and 3 c are alternately provided in this order along theaxial direction of the inner yoke 2 (i.e., along a movement direction ofthe mover 31). In FIG. 10, open arrows indicate magnetization directionsof the respective flat plate magnets 3 a and 3 c. Each flat plate magnet(first flat plate magnet) 3 a is a flat plate permanent magnetmagnetized from inside to outside in a direction perpendicular to theouter surface of the inner yoke 2. On the other hand, each flat platemagnet (second flat plate magnet) 3 c is a flat plate permanent magnetmagnetized from outside to inside in a direction perpendicular to theouter surface of the inner yoke 2. Hence, the magnetization directionsof the flat plate magnets 3 a and 3 c are perpendicular to the outersurface of the inner yoke 2 and are opposite to each other.

Furthermore, positions of the flat plate magnets 3 a and 3 c provided atthe outer surfaces of the inner yoke 2 are deviated from each other by adimension equal to or less than ¼ of a total length of one set of thetwo types of the flat plate magnets 3 a and 3 c. In the exampleillustrated in FIG. 10, at the four outer surfaces of the quadrangulartubular inner yoke 2, the positions of the flat plate magnets 3 a and 3c provided at the two opposing outer surfaces coincide with each other,but the positions of the flat plate magnets 3 a and 3 c provided at thetwo adjacent outer surfaces are deviated from each other.

A structure of an armature according to the third embodiment is similarto that of the armature 4 according to the first embodiment describedabove (see FIGS. 2A to 2C and FIGS. 3A and 3B).

Also in a linear motor according to the third embodiment, the armature 4functions as a stator, and currents are passed through the windings 8 aand 8 b in opposite directions, thus causing a reciprocating linearmotion of the mover 31, passed through the hollow portion 9 of thearmature 4, with respect to the armature 4 (stator). In this case, thepositions of the flat plate magnets 3 a and 3 c provided at the adjacentouter surfaces of the inner yoke 2 of the mover 31 are deviated fromeach other in the axial direction of the inner yoke 2 (i.e., in themovement direction of the mover 31). Hence, the effect of reducingthrust ripple and/or detent force can be achieved, thereby eliminatingcogging and realizing a smooth linear movement of the mover 31.

Note that although five sets of the flat plate magnets 3 a and 3 c,i.e., a total of ten flat plate magnets, are provided sequentially in acontinuous manner at each outer surface, such a structure is provided byway of example, and the number of the flat plate magnets may be anynumber. Furthermore, although the shape of the inner yoke 2 is aquadrangular tubular shape, this shape is provided by way of example,and the inner yoke 2 may have a different polygonal tubular shape suchas an octagonal tubular shape. At the four outer surfaces of thequadrangular tubular inner yoke 2, the positions of the flat platemagnets 3 a and 3 c provided at the two opposing outer surfaces coincidewith each other, and the positions of the flat plate magnets 3 a and 3 cprovided at the two adjacent outer surfaces are deviated from eachother. However, the positions of the flat plate magnets 3 a and 3 cprovided at the four outer surfaces of the inner yoke 2 may be slightlydeviated from each other so that all the positions are different. It isto be noted that even in such a structure example, a maximum deviationamount is equal to or less than ¼ of a length of one set of the two flatplate magnets 3 a and 3 c.

Fourth Embodiment

In a fourth embodiment, two-phase drive is carried out by a single coreunit. In the foregoing first or third embodiment, three-phase drive iscarried out, and therefore, three armatures are linearly provided sothat the mover is passed therethrough. Accordingly, there arises aproblem that the resulting linear motor has a large total length. In thefourth embodiment described below, two-phase drive is carried out by asingle core unit, thus significantly solving the problem of a largetotal length, which has been present in a three-phase separateindependent type linear motor.

FIG. 11 is a perspective view illustrating a structure of a moveraccording to the fourth embodiment of the present invention. A mover 41is formed so that four types of flat plate magnets 3 a, 3 b, 3 c and 3 dare alternately provided in this order at each of four outer surfaces 2a, 2 b, 2 c and 2 d of a quadrangular tubular inner yoke 2, made of asoft magnetic material, along an axial direction of the inner yoke 2(i.e., along a movement direction of the mover 41). In FIG. 11, openarrows indicate magnetization directions of the respective flat platemagnets 3 a, 3 b, 3 c and 3 d. Each flat plate magnet (first flat platemagnet) 3 a is a flat plate permanent magnet magnetized from inside tooutside in a direction perpendicular to the outer surface of the inneryoke 2. On the other hand, each flat plate magnet (second flat platemagnet) 3 c is a flat plate permanent magnet magnetized from outside toinside in a direction perpendicular to the outer surface of the inneryoke 2. Hence, the magnetization directions of the flat plate magnets 3a and 3 c are perpendicular to the outer surface of the inner yoke 2 andare opposite to each other.

Further, the flat plate magnets 3 b and 3 d are flat plate permanentmagnets each magnetized from the adjacent flat plate magnet 3 c to theadjacent flat plate magnet 3 a along the axial direction of the inneryoke 2 (i.e., along a longitudinal direction of the outer surfacethereof). Hence, the magnetization directions of the flat plate magnets3 b and 3 d correspond to the axial direction of the inner yoke 2 andare opposite to each other.

Furthermore, positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the two upper adjacent outer surfaces 2 a and 2 b of theinner yoke 2, and positions of the flat plate magnets 3 a, 3 b, 3 c and3 d provided at the two lower adjacent outer surfaces 2 c and 2 d of theinner yoke 2 are deviated from each other by a dimension of ¼ of a totallength of one set of the four types of the flat plate magnets 3 a, 3 b,3 c and 3 d (i.e., by λ/4 where λ denotes a field cycle, or by anelectrical angle of)90°.

A structure of an armature according to the fourth embodiment is similarto that of the armature 4 according to the first embodiment describedabove (see FIGS. 2A to 2C and FIGS. 3A and 3B), and therefore, thedetailed description thereof will be omitted.

FIG. 12 is a perspective view illustrating a structure of a linear motor50 according to the fourth embodiment, and FIG. 13 is a partially brokenperspective view illustrating the structure of the linear motor 50. Anarmature 4 is formed by alternately arranging and stacking single poleunits and spacer units in the following order: a first single pole unit5A, a spacer unit 11A, a second single pole unit 6A, a spacer unit 11C,a first single pole unit 5B, a spacer unit 11B and a second single poleunit 6B. Moreover, the foregoing mover 41 illustrated in FIG. 11 ispassed through a hollow portion 9 formed by continuous openings 5 a and6 a of the armature 4 (see FIG. 3B), thus forming a two-phase drivelinear motor 50 according to the fourth embodiment.

In this case, the mover 41 is passed through the hollow portion 9 of thearmature 4 so that the upper adjacent outer surfaces 2 a and 2 b of theinner yoke 2 of the mover 41 are opposed to upper core portions 5 c ofthe first single pole units 5A and 5B (i.e., an upper winding 8 aserving as a first winding), and the lower adjacent outer surfaces 2 cand 2 d of the inner yoke 2 are opposed to lower core portions 5 c ofthe first single pole units 5A and 5B (i.e., a lower winding 8 b servingas a second winding).

Further, a sinusoidal wave current is passed through the winding 8 a anda cosine wave current is passed through the winding 8 b so that anenergization phase difference of 90° occurs between the windings 8 a and8 b. Also in this linear motor 50, the armature 4 functions as a stator.Currents by which a phase difference of 90° occurs are passed throughthe windings 8 a and 8 b, thus making it possible to continuouslyproduce thrust force for the mover 41 passed through the hollow portion9 of the armature 4, and causing a reciprocating linear motion of themover 41 with respect to the armature 4 (stator). In this case, thrustforce peaks can be obtained alternately at the upper and lower coreportions 5 c of the armature 4, thereby making it possible to obtaincontinuous thrust force by a single core unit and to implement thetwo-phase drive linear motor 50.

In the three-phase independent type linear motor according to the firstor third embodiment described above, the three armatures are necessary,and interphase space for phase adjustment has to be provided between thearmatures adjacent to each other, thus causing a problem that theresulting total length is increased. On the other hand, in the linearmotor according to the fourth embodiment described above, a movement ofthe mover is enabled with the use of a single armature, and therefore,the resulting total length can be considerably reduced. Hence, thelinear motor can be used even in a narrow region, thereby increasing therange of use of the linear motor.

Naturally, the fourth embodiment also has advantages similar to thosedescribed in the first and third embodiments. Specifically, since thespacer units 11A, 11B and 11C are inserted between the adjacent singlepole units, the thickness of the core portion in each single pole unitdoes not have to be smaller than that of the yoke portion and thus noadditional process is necessary, so that the use of the single poleunits having a uniform thickness as a whole is enabled, therebysimplifying a fabrication process. Furthermore, in a conventionalcylindrical linear motor that uses, for example, a structure in which aradially magnetized cylindrical magnet is adhered to a solid inner yokeor a structure in which an axially magnetized cylindrical magnet isadhered to a solid inner yoke, the inner yoke is large and the mass of amover is increased, thus making it difficult to achieve a high-speedresponsiveness. However, in the mover 41 according to the fourthembodiment, the inner yoke 2 is hollow; furthermore, a reduction inmagnetic flux generated inside the inner yoke 2 is enabled, and areduction in thickness of the cornered tubular inner yoke 2 is enabled,thus enabling a reduction in weight of the mover 41. Hence, an increasein the response speed of the mover 41 is enabled.

Besides, examples of methods for reducing the thickness of an inner yokeof a mover include a method for reducing a magnet pole pitch; however,when a pole pitch is reduced, the number of areas where windings arelocated is increased in a structure of a conventional armature, and theresulting shape tends to increase in size. On the other hand, in thearmature 4 according to the fourth embodiment, a winding is not woundfor each pole but the windings 8 a and 8 b are collectively wound;therefore, even when a magnetic pole pitch is small, a winding structureis not complicated but is simply provided, thus facilitating sizereduction.

Further, since the mover 41 has a quadrangular cross-sectional shape inthe linear motor 50 according to the fourth embodiment, magnets can beprovided at four surfaces in a divided manner, and in addition, the useof flat plate magnets is enabled. Hence, as compared with a cylindricallinear motor, fabrication flexibility, including selection of magnets tobe used, is extremely high, and the fabrication of the mover 41 havinghigh rigidity can be easily carried out. In addition, the directions ofsides of the openings 5 a and 6 a of the single pole units 5A and 5B and6A and 6B are inclined by 45° with respect to the directions of sides ofmain bodies of the first and second single pole units 5A and 5B and 6Aand 6B Hence, the flow of magnetic flux through the armature 4 issmoothed, thus making it difficult to cause magnetic saturation.

Note that although five sets of the flat plate magnets 3 a, 3 b, 3 c and3 d, i.e., a total of twenty flat plate magnets, are providedsequentially in a continuous manner at each outer surface, such astructure is provided by way of example, and the number of the flatplate magnets may be any number. Further, although two sets of the firstand second single pole units 5A and 5B and 6A and 6B are alternatelyarranged, this arrangement is provided by way of example, and the numberof sets may be any number. Furthermore, although sinusoidal wave currentand cosine wave current are passed through the windings 8 a and 8 b,respectively, these currents are provided for illustrative purposes, andany current may be passed through each of the windings 8 a and 8 b aslong as a phase difference of an electrical angle of 90° occurs. Forexample, the waveforms of currents passed through the windings 8 a and 8b may be rectangular waveforms or trapezoidal waveforms by which a phasedifference of an electrical angle of 90° occurs.

Actually, a two-phase drive linear motor conventionally has a problemthat thrust ripple and detent force are increased, and it is feared thatthis problem might occur also in the fourth embodiment. Hereinafter,methods for reducing thrust ripple and detent force in the fourthembodiment will be described. In the fourth embodiment, the arrangementof the flat plate magnets in the mover 41 and spacing between magneticpole teeth of the armature 4 are adjusted, thereby reducing thrustripple and detent force which cause problems in a two-phase drive linearmotor.

In a two-phase drive linear motor, harmonic components of thrust rippleand detent force are increased for each of the second-order,fourth-order, sixth-order and eighth-order harmonics. Therefore,ingenious methods for reducing harmonic components of the respectiveorders will each be described. The following examples are based on theprinciple that mutual cancellation occurs upon addition of twosinusoidal waves whose phases are deviated by 180° and mutualcancellation occurs upon addition of two cosine waves whose phases aredeviated by 180°.

<Reduction of Second-Order and Sixth-Order Harmonic Components>

FIG. 14 is a cross-sectional view of a standard armature 4. As mentionedabove (see FIGS. 12 and 13), the armature 4 is formed by alternatelyarranging and combining single pole units and spacer units in thefollowing order: a first single pole unit 5A, a spacer unit 11A, asecond single pole unit 6A, a spacer unit 11C, a first single pole unit5B, a spacer unit 11B and a second single pole unit 6B. In the exampleof FIG. 14, the three spacer units 11A, 11B and 11C have the samethickness, and the first single pole unit 5A, the second single poleunit 6A, the first single pole unit 5B and the second single pole unit6B are equidistantly arranged. Note that a set of the first single poleunit 5A, the spacer unit 11A and the second single pole unit 6A will bereferred to as a “first block 51”, and a set of the first single poleunit 5B, the spacer unit 11B and the second single pole unit 6B will bereferred to as a “second block 52”.

FIG. 15 is a cross-sectional view of the armature 4 for describing amethod for reducing second-order and sixth-order harmonic components. InFIG. 15, spacing is extended by an electrical angle of 90° with respectto the equidistant arrangement of the single pole units illustrated inFIG. 14. Specifically, spacing between the first and second blocks 51and 52 (i.e., spacing between the second single pole unit 6A and thefirst single pole unit 5B) is extended by an electrical angle of 90°(i.e., by a length of λ/4 where λ denotes a field cycle), and is thusgreater than spacing between the first and second single pole units 5Aand 6A and spacing between the first and second single pole units 5B and6B. Such a structure can be easily achieved by increasing the thicknessof the spacer unit 11C (i.e., by using a thicker spacer unit 11C) ascompared with the example illustrated in FIG. 14.

By extending the spacing between the first and second blocks 51 and 52by an electrical angle of 90°, a deviation of 180° (=90°×2) occurs forthe second-order harmonic, and cancellation occurs due to additionbetween the first and second blocks 51 and 52, thereby reducing thesecond-order harmonic component. Further, a deviation of 540° (=90°×6)occurs for the sixth-order harmonic, and cancellation occurs between theblocks, thereby also reducing the sixth-order harmonic component. Thespacing between the first and second blocks 51 and 52 (i.e., the spacingbetween magnetic pole teeth) is adjusted in this manner, thus reducingthe second-order and sixth-order harmonic components of thrust rippleand detent force.

<Reduction of Fourth-Order Harmonic Component>

FIG. 16 is a perspective view of the mover 41 for describing a methodfor reducing a fourth-order harmonic component. While a state where thepositions of the flat plate magnets 3 a, 3 b, 3 c and 3 d provided atthe upper outer surfaces 2 a and 2 b of the inner yoke 2 and thepositions of the flat plate magnets 3 a, 3 b, 3 c and 3 d provided atthe lower outer surfaces 2 c and 2 d are deviated from each other by anelectrical angle of 90° (i.e., by a length of λ/4) is maintained, thepositions of the flat plate magnets 3 a, 3 b, 3 c and 3 d provided atthe upper outer surface 2 a and the positions of the flat plate magnets3 a, 3 b, 3 c and 3 d provided at the upper outer surface 2 b aredeviated from each other by an electrical angle of 45° (i.e., by alength of λ/8); in addition, the positions of the flat plate magnets 3a, 3 b, 3 c and 3 d provided at the lower outer surface 2 c and thepositions of the flat plate magnets 3 a, 3 b, 3 c and 3 d provided atthe lower outer surface 2 d are deviated from each other by anelectrical angle of 45° (i.e., by a length of λ/8).

By deviating the positions of the flat plate magnets provided at theadjacent outer surfaces by an electrical angle of 45°, a deviation of180° (=45°×4) occurs for the fourth-order harmonic, and cancellationoccurs due to addition between the adjacent outer surfaces, therebyreducing the fourth-order harmonic component. The positions of the flatplate magnets 3 a, 3 b, 3 c and 3 d provided at the outer surfaces ofthe inner yoke 2 are adjusted in this manner, thus reducing eachfourth-order harmonic component of thrust ripple and detent force.

<Reduction of Eighth-Order Harmonic Component>

FIG. 17 is a cross-sectional view of the armature 4 for describing amethod for reducing an eighth-order harmonic component. The spacingbetween the first and second single pole units 5A and 6A and the spacingbetween the first and second single pole units 5B and 6B are eachextended (see open arrows) by an electrical angle of 22.5° (i.e., by alength of λ/16) without any change in centers of gravity of the firstand second blocks 51 and 52 after the above-described adjustment of thethickness of the spacer unit 11C, which is illustrated in FIG. 15. Sucha structure can be easily achieved by increasing the thicknesses of thespacer units 11A and 11B (i.e., by using thicker spacer units 11A and11B).

By extending the spacing between the first and second single pole unitsby an electrical angle of 22.5°, a deviation of 180° (=22.5°×8) occursfor the eighth-order harmonic, and cancellation occurs due to additionbetween the adjacent single pole units, thereby reducing theeighth-order harmonic component. The spacing between the first andsecond single pole units (i.e., the spacing between magnetic pole teeth)in both of the blocks is adjusted in this manner, thus reducing theeighth-order harmonic component of thrust ripple and detent force.

Note that the foregoing method (first reduction method) is provided byway of example, and methods for reducing harmonic components of therespective orders of thrust ripple and detent force are not limited tothe foregoing method; alternatively, other methods may be used. Othermethods for reducing harmonic components of the respective orders willbe described below.

(Second Reduction Method)

In this method, the second-order and sixth-order harmonic components ofthrust ripple and detent force are reduced by adjusting the magnetarrangement of the mover, the fourth-order harmonic component is reducedby adjusting the spacing between the blocks of the armature, and theeighth-order harmonic component is reduced by adjusting the spacingbetween the first and second single pole units in each block.

(Third Reduction Method)

In this method, the second-order and sixth-order harmonic components ofthrust ripple and detent force are reduced by adjusting the spacingbetween the blocks of the armature, the fourth-order harmonic componentis reduced by adjusting the spacing between the first and second singlepole units in each block, and the eighth-order harmonic component isreduced by adjusting the magnet arrangement of the mover.

Fifth Embodiment

In the fourth embodiment, the flat plate magnets 3 b and 3 d magnetizedin the axial direction of the mover may be removed similarly to thethird embodiment.

Specifically, the mover is formed so that the two types of the flatplate magnets 3 a and 3 c are alternately provided in this order at eachof the outer surfaces 2 a to 2 d of the quadrangular tubular inner yoke2, made of a soft magnetic material, along the axial direction of theinner yoke 2 (i.e., along the movement direction of the mover), and thepositions of the flat plate magnets 3 a and 3 c provided at the upperouter surfaces 2 a and 2 b of the inner yoke 2, and the positions of theflat plate magnets 3 a and 3 c provided at the lower outer surfaces 2 cand 2 d of the inner yoke 2 are deviated from each other by a dimensionequal to or less than ¼ of a length of one set of the two types of theflat plate magnets 3 a and 3 c (i.e., by λ/4 where λ denotes a fieldcycle, or by an electrical angle of 90°).

Further, in order to reduce the second-order, fourth-order, sixth-orderand eighth-order harmonic components of thrust ripple and detent force,similarly to the fourth embodiment described above, the followingmeasures are taken. While a state where the positions of the flat platemagnets 3 a and 3 c provided at the upper outer surfaces 2 a and 2 b ofthe inner yoke 2 and the positions of the flat plate magnets 3 a and 3 cprovided at the lower outer surfaces 2 c and 2 d are deviated from eachother by an electrical angle of 90° is maintained, the positions of theflat plate magnets 3 a and 3 c provided at the upper outer surface 2 aand the positions of the flat plate magnets 3 a and 3 c provided at theupper outer surface 2 b are deviated from each other by a predeterminedelectrical angle (by 90° for the second-order and sixth-order harmoniccomponents, by 45° for the fourth-order harmonic component, and by 22.5°for the eighth-order harmonic component); in addition, the positions ofthe flat plate magnets 3 a and 3 c provided at the lower outer surface 2c and the positions of the flat plate magnets 3 a and 3 c provided atthe lower outer surface 2 d are deviated from each other by apredetermined electrical angle (by 90° for the second-order andsixth-order harmonic components, by 45° for the fourth-order harmoniccomponent, and by 22.5° for the eighth-order harmonic component).

Note that also in the foregoing fourth and fifth embodiments, similarlyto the second embodiment, linear guide rails 12 may be provided at twocorner portions of the outer surfaces of the inner yoke 2 of the mover41 so as to be extended (see FIG. 7), and cut-outs for allowing thelinear guide rails 12 to pass through the openings of the first andsecond single pole units 5 and 6 constituting the armature 4 may beprovided.

Hereinafter, specific structures of linear motors fabricated by thepresent inventor and characteristics of the fabricated linear motorswill be described.

(Example of First Embodiment)

First, as the mover 1 used for a linear motor, a mover including aquadrangular tubular inner yoke and flat plate permanent magnets asillustrated in FIG. 1 was fabricated. The inner yoke 2 to be used ismade of pure iron and has a quadrangular tubular form with an outershape of 22 mm per side and an inner shape of 18 mm per side.

Ten sets of the flat plate magnets 3 a, 3 b, 3 c and 3 d, in which eachset includes the four types of the flat plate magnets 3 a, 3 b, 3 c and3 d, are adhered to each of the four outer surfaces of the foregoinginner yoke 2 so as to be continuous in the axial direction of the inneryoke 2 (i.e., in the movement direction of the mover 1). Each flat platemagnet 3 a is a permanent magnet having a length of 10 mm, a width of 22mm and a height of 4 mm and magnetized from inside (axial center of themovement direction) to outside in a height direction of the mover 1, andeach flat plate magnet 3 c is a permanent magnet having a length of 10mm, a width of 22 mm and a height of 4 mm and magnetized from outside toinside in the height direction of the mover 1. The magnetizationdirections of the flat plate magnets 3 a and 3 c correspond to theheight direction (i.e., the direction perpendicular to the outer surfaceof the inner yoke 2) but are opposite to each other (see the open arrowsin FIG. 1).

Furthermore, each flat plate magnet 3 b is a permanent magnet having alength of 2 mm, a width of 22 mm and a height of 4 mm and magnetizedfrom the flat plate magnet 3 c to the flat plate magnet 3 a in alongitudinal direction of the mover 1, and each flat plate magnet 3 d isa permanent magnet having a length of 2 mm, a width of 22 mm and aheight of 4 mm and magnetized from the flat plate magnet 3 c to the flatplate magnet 3 a in the longitudinal direction of the mover 1. Themagnetization directions of the flat plate magnets 3 b and 3 dcorrespond to the longitudinal direction (i.e., the movement directionof the mover 1) but are opposite to each other (see the open arrows inFIG. 1).

Hence, a length of the ten sets of the flat plate magnets 3 a, 3 b, 3 cand 3 d , i.e., a total of forty flat plate magnets which are continuouswith each other, is 240 mm (=(10 mm+2 mm+10 mm+2 mm)×10). The positionsof the flat plate magnets 3 a, 3 b, 3 c and 3 d provided at the adjacentouter surfaces of the inner yoke 2 are deviated from each other by alength of the flat plate magnet 3 b or 3 d (2 mm).

Next, the armature 4 was fabricated. Sixteen armature materials eachhaving a shape illustrated in FIG. 18A were cut out from a silicon steelplate having a thickness of 0.5 mm, and the cut-out sixteen armaturematerials were stacked and adhered to each other, thus fabricating thefirst single pole unit 5 or second single pole unit 6 having a thicknessof 8 mm (see FIGS. 2A and 2B). Further, eight armature materials eachhaving a shape illustrated in FIG. 18B were cut out from a silicon steelplate having a thickness of 0.5 mm, and the cut-out eight armaturematerials were stacked and adhered to each other, thus fabricating thespacer unit 11 having a thickness of 4 mm (see FIG. 2C).

A single-phase unit (see FIG. 3A) was formed by stacking the respectiveunits fabricated as described above in the following order: the firstsingle pole unit 5, the spacer unit 11, the second single pole unit 6,the spacer unit 11, the first single pole unit 5, the spacer unit 11,and the second single pole unit 6. This single-phase unit has athickness of 44 mm (=8 mm×4+4 mm×3). Furthermore, a magnetic pole pitchis 12 mm (=8 mm+4 mm).

For the single-phase unit, the windings 8 a and 8 b serving as drivecoils are provided as follows. Through gap portions at four corners, apolyimide tape was wound around portions of an armature core, where thewindings are to be wound, in order to ensure insulation, and a conductorwas wound 100 turns over the tape at each of two areas (see FIG. 3B).Then, serial connection was made so that directions of currents areopposite to each other upon energization.

The three armatures 4 fabricated in this manner were prepared, the threearmatures 4 were linearly arranged at intervals of 20 mm (=12 mm×(1+⅔)),the mover 1 was inserted into the center hollow portion (see FIG. 4),and the armatures 4 were fixed to a test bench so that the mover 1 wasmovable in the longitudinal direction without coming into contact withthe armatures 4.

One ends of a pair of the drive coils wound around the three armatures 4were connected to each other, and the other ends thereof were connectedwith U, V and W phases of a three-phase power source, thereby providinga star connection and making a connection to a motor controller.Furthermore, an optical linear scale was adhered to a tip portion of themover 1, and a linear encoder was attached to a region fixed to the testbench, thereby allowing the position of the mover 1 to be read.Moreover, a position signal detected by the linear encoder was outputtedto the motor controller to control the position of the mover 1.

After the connections were made as described above, the thrust force ofthe mover 1 was measured while drive current applied to the drive coilswas changed. In this case, the thrust force was measured using a methodin which a force gage was pressed against the mover 1. Results of themeasurement are illustrated in FIG. 19. The horizontal axis in FIG. 19represents a value obtained by the following expression: an rms value ofthe drive current×the number of turns of the coils per phase of thearmature.

As illustrated in FIG. 19, a maximum thrust force of more than 700 N wasobtained. Since the mass of the mover 1 was 1.1 kg, a thrust force/movermass ratio was 637 N/kg. In a conventional linear motor operated in theother mode in which a thrust force of 700 N is obtained (Japanese PatentApplication Laid-Open No. 2002-359962), the mass of a mover has to be 3kg or more, and therefore, a thrust force/mover mass ratio is 233 N/kgor less. In obtaining the same level of thrust force, the linear motorof the present invention is capable of reducing the mass of the mover toabout ⅓ as compared with the conventional linear motor. Thus, thepresent invention can provide a linear motor extremely effective inperforming a high-speed process in a finishing machine or the like.

(Example of Fourth Embodiment)

An example of the fourth embodiment in which two-phase drive is carriedout by a single core unit will be described. FIGS. 20A, 20B and 20C area top view, a side view and a cross-sectional view illustrating a statein which the mover 41 is passed through the armature 4. In this example,the linear guide rails 12, linear guide sliders 13 and mover supportframes 14, which have been described in the second embodiment, areprovided.

First, as the mover 41 used for a linear motor, a mover including aquadrangular tubular inner yoke and flat plate permanent magnets asillustrated in FIG. 11 was fabricated. The inner yoke 2 to be used ismade of pure iron and has a quadrangular tubular form with an outershape of 32 mm per side and an inner shape of 26 mm per side. Aplurality of sets of the flat plate magnets 3 a, 3 b, 3 c and 3 d, inwhich each set includes the four types of the flat plate magnets 3 a, 3b, 3 c and 3 d, are adhered to each of the four outer surfaces 2 a to 2d of the foregoing inner yoke 2 so as to be continuous in the axialdirection of the inner yoke 2 (i.e., in the movement direction of themover 41). Each flat plate magnet 3 a is a permanent magnet having alength of 10 mm, a width of 25 mm and a height of 4 mm and magnetizedfrom inside (axial center of the movement direction) to outside in aheight direction of the mover 41, and each flat plate magnet 3 c is apermanent magnet having a length of 10 mm, a width of 25 mm and a heightof 4 mm and magnetized from outside to inside in the height direction ofthe mover 41. The magnetization directions of the flat plate magnets 3 aand 3 c correspond to the height direction (i.e., the directionperpendicular to the outer surface of the inner yoke 2) but are oppositeto each other (see the open arrows in FIG. 11).

Furthermore, each flat plate magnet 3 b is a permanent magnet having alength of 2 mm, a width of 25 mm and a height of 4 mm and magnetizedfrom the flat plate magnet 3 c to the flat plate magnet 3 a in alongitudinal direction of the mover 41, and each flat plate magnet 3 dis a permanent magnet having a length of 2 mm, a width of 25 mm and aheight of 4 mm and magnetized from the flat plate magnet 3 c to the flatplate magnet 3 a in the longitudinal direction of the mover 41. Themagnetization directions of the flat plate magnets 3 b and 3 dcorrespond to the longitudinal direction (i.e., the movement directionof the mover 41) but are opposite to each other (see the open arrows inFIG. 11).

The positions of the flat plate magnets 3 a, 3 b, 3 c and 3 d providedat the upper adjacent outer surfaces 2 a and 2 b of the inner yoke 2,and the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the lower adjacent outer surfaces 2 c and 2 d of the inneryoke 2 are deviated from each other by 6 mm in the movement direction(axial direction) of the mover 41. A total length of one set of the fourtypes of the flat plate magnets 3 a, 3 b, 3 c and 3 d is 24 mm, and thedeviation of 6 mm corresponds to a deviation equivalent to a dimensionof ¼ of a magnet arrangement cycle of 24 mm, which is a field cycle (λ)(λ/4: an electrical angle of 90°).

Moreover, the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the upper outer surface 2 a and the positions of the flatplate magnets 3 a, 3 b, 3 c and 3 d provided at the upper outer surface2 b are deviated from each other by 3 mm in the movement direction ofthe mover 41, and the positions of the flat plate magnets 3 a, 3 b, 3 cand 3 d provided at the lower outer surface 2 c and the positions of theflat plate magnets 3 a, 3 b, 3 c and 3 d provided at the lower outersurface 2 d are deviated from each other by 3 mm in the movementdirection of the mover 41. The deviation of 3 mm corresponds to adeviation equivalent to an electrical angle of 45° (i.e., a dimension ofλ/8, which is ⅛ of a field cycle (λ) of 24 mm) described with referenceto FIG. 16. Thus, the mover 41 having a length of 141 mm, a width of 25mm and a height of 4 mm was fabricated.

Next, the armature 4 was fabricated. Armature materials each having ashape illustrated in FIG. 21A were cut out from a silicon steel platehaving a thickness of 0.5 mm, and the cut-out twenty armature materialswere stacked and adhered to each other, thus fabricating the firstsingle pole unit 5 (5A or 5B) or second single pole unit 6 (6A or 6B)having a thickness of 10 mm. Further, armature materials each having ashape illustrated in FIG. 21B were cut out from a silicon steel platehaving a thickness of 0.5 mm, and the cut-out seven armature materialswere stacked and adhered to each other, thus fabricating each of the twospacer units 11 (spacer units 11A and 11B) each having a thickness of3.5 mm; in addition, the cut-out thirteen armature materials werestacked and adhered to each other, thus fabricating the single spacerunit 11 (spacer unit 11C) having a thickness of 6.5 mm.

A core unit having a length of 80 mm, a width of 80 mm and a height of53.5 mm (=10 mm×4+3.5 mm×2+6.5 mm×1) was formed by stacking therespective units fabricated as described above in the following order:the first single pole unit 5A, the spacer unit 11A, the second singlepole unit 6A, the spacer unit 11C, the first single pole unit 5B, thespacer unit 11B, and the second single pole unit 6B. Note that thethicknesses of the foregoing spacer units 11A, 11B and 11C areappropriately set with the aim of reducing the second-order, sixth-orderand eighth-order harmonic components of thrust ripple and detent forceand in order to adjust the spacing between the magnetic pole teethdescribed with reference to FIGS. 15 and 17.

FIG. 22 provides a cross-sectional view of a core unit provided by thefirst reduction method. In this example, with the aim of reducing thesecond-order and sixth-order harmonic components of thrust ripple anddetent force, the spacing between the blocks 51 and 52 is extended by 6mm equivalent to λ/4 (electrical angle of 90°) where the field cycle isrepresented by λ(=24 mm); furthermore, with the aim of reducing theeighth-order harmonic component, the spacing between the first andsecond single pole units 5A and 6A and the spacing between the first andsecond single pole units 5B and 6B (i.e., the spacing between magneticpole teeth) in the respective blocks 51 and 52 are each extended by 1.5mm equivalent to λ/16 (electrical angle of22.5°). As a result, when thethickness of a basic spacer unit is 2 mm, the thicknesses of the spacerunits 11A and 11B are each set at 3.5 mm, and the thickness of thespacer unit 11C is set at 6.5 mm.

For the core unit, the windings 8 a and 8 b serving as drive coils areprovided as follows. Through gap portions at four corners, a polyimidetape was wound around portions of an armature core, where the windingsare to be wound, in order to ensure insulation, and a conductor waswound 100 turns over the tape at each of two areas. Then, sinusoidalwave drive current and cosine wave drive current are applied to thewindings 8 a and 8 b, respectively.

The two drive coils of the armature described above were connected to atwo-phase drive motor controller, a position sensor was attached to atip of the mover, and a position signal is inputted to the two-phasedrive motor controller, thereby measuring thrust characteristics of thelinear motor. Results of the measurement are illustrated in FIG. 23. Thehorizontal axis in FIG. 23 represents a value obtained by the followingexpression: an rms value of the drive current×the number of turns of thecoils.

As illustrated in FIG. 23, a thrust force of about 160 N is obtained ina range in which the thrust force is proportional to the drive current,and a maximum thrust force of more than 200 N is obtained. In the fourthembodiment, such excellent characteristics are achieved with the use ofthe armature having a total length of only about 65 mm.

In the phase independent type linear motor serving as a conventionalexample (Japanese Patent Application Laid-open No. 2008-228545) or theforegoing three-phase drive linear motor, an armature needs to have atotal length of about 150 mm in order to obtain thrust characteristicssimilar to those obtained in the fourth embodiment, but in the fourthembodiment, the total armature length can be reduced by one-half ormore. Since size reduction and space saving can be achieved as describedabove, the linear motor according to the fourth embodiment is mostsuitable for use in a superposed manner as in an X-Y-Z-axis triaxialdrive stage.

(Example of Second Reduction Method)

In the second reduction method, the second-order and sixth-orderharmonic components of thrust ripple and detent force are reduced byadjusting the magnet arrangement of the mover 41, the fourth-orderharmonic component is reduced by adjusting the spacing between theblocks 51 and 52 of the armature 4, and the eighth-order harmoniccomponent is reduced by adjusting the spacing between the first andsecond single pole units 5A and 6A in the block 51 and the spacingbetween the first and second single pole units 5B and 6B in the block52.

The positions of the flat plate magnets 3 a, 3 b, 3 c and 3 d providedat the upper adjacent outer surfaces 2 a and 2 b of the inner yoke 2,and the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the lower adjacent outer surfaces 2 c and 2 d of the inneryoke 2 are deviated from each other by 6 mm (λ/4: an electrical angleof90°) in the movement direction (axial direction) of the mover 41;besides, the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the upper outer surface 2 a and the positions of the flatplate magnets 3 a, 3 b, 3 c and 3 d provided at the upper outer surface2 b are deviated from each other by 6 mm (λ/4: an electrical angleof90°) in the movement direction of the mover 41, and the positions ofthe flat plate magnets 3 a, 3 b, 3 c and 3 d provided at the lower outersurface 2 c and the positions of the flat plate magnets 3 a, 3 b, 3 cand 3 d provided at the lower outer surface 2 d are deviated from eachother by 6 mm (λ/4: an electrical angle of90°) in the movement directionof the mover 41.

FIG. 24 provides a cross-sectional view of the core unit provided by thesecond reduction method. In this example, with the aim of reducing thefourth-order harmonic component of thrust ripple and detent force, thespacing between the blocks 51 and 52 is extended by 3 mm equivalent toλ/8 (electrical angle of 45°) where the field cycle is represented by λ(=24 mm); furthermore, with the aim of reducing the eighth-orderharmonic component, the spacing between the first and second single poleunits 5A and 6A and the spacing between the first and second single poleunits 5B and 6B (i.e., the spacing between magnetic pole teeth) in therespective blocks 51 and 52 are each extended by 1.5 mm equivalent toλ/16 (electrical angle of 22.5°). As a result, the spacing betweenmagnetic pole teeth is equally extended by 1.5 mm. In this core unit,the spacer units 11A, 11B and 11C each have a thickness of 3.5 mm, and aheight of the entire core unit is 50.5 mm (=10 mm×4+3.5 mm×3).

(Example of Third Reduction Method)

In this method, the second-order and sixth-order harmonic components ofthrust ripple and detent force are reduced by adjusting the spacingbetween the blocks 51 and 52 of the armature 4, the fourth-orderharmonic component is reduced by adjusting the spacing between the firstand second single pole units 5A and 6A in the block 51 and the spacingbetween the first and second single pole units 5B and 6B in the block52, and the eighth-order harmonic component is reduced by adjusting themagnet arrangement of the mover 41.

FIG. 25 provides a cross-sectional view of the core unit provided by thethird reduction method. In this example, with the aim of reducing thesecond-order and sixth-order harmonic components of thrust ripple anddetent force, the spacing between the blocks 51 and 52 is extended by 6mm equivalent to λ/4 (electrical angle of 90°) where the field cycle isrepresented by λ (=24 mm); furthermore, with the aim of reducing thefourth-order harmonic component, the spacing between the first andsecond single pole units 5A and 6A and the spacing between the first andsecond single pole units 5B and 6B (i.e., the spacing between magneticpole teeth) in the respective blocks 51 and 52 are each extended by 3 mmequivalent to λ/8 (electrical angle of 45°). As a result, the spacingbetween magnetic pole teeth is equally extended by 3 mm. In this coreunit, the spacer units 11A, 11B and 11C each have a thickness of 5 mm,and a height of the entire core unit is 55 mm (=10 mm×4+5 mm×3).

Moreover, the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the upper adjacent outer surfaces 2 a and 2 b of the inneryoke 2, and the positions of the flat plate magnets 3 a, 3 b, 3 c and 3d provided at the lower adjacent outer surfaces 2 c and 2 d of the inneryoke 2 are deviated from each other by 6 mm (λ/4; an electrical angleof90°) in the movement direction (axial direction) of the mover 41;besides, the positions of the flat plate magnets 3 a, 3 b, 3 c and 3 dprovided at the upper outer surface 2 a and the positions of the flatplate magnets 3 a, 3 b, 3 c and 3 d provided at the upper outer surface2 b are deviated from each other by 1.5 mm (λ/16: an electrical angle of22.5°) in the movement direction of the mover 41, and the positions ofthe flat plate magnets 3 a, 3 b, 3 c and 3 d provided at the lower outersurface 2 c and the positions of the flat plate magnets 3 a, 3 b, 3 cand 3 d provided at the lower outer surface 2 d are deviated from eachother by 1.5 mm (λ/16: an electrical angle of 22.5°) in the movementdirection of the mover 41.

(Example of Fifth Embodiment)

Two drive coils of the armature fabricated similarly to the example ofthe fourth embodiment described above were connected to a two-phasemotor controller, a position sensor was attached to a tip of the mover,and a position signal is inputted to the two-phase drive motorcontroller, thereby measuring thrust characteristics of the linearmotor. Results of the measurement are illustrated in FIG. 26. Thehorizontal axis in FIG. 26 represents a value obtained by the followingexpression: an rms value of the drive current×the number of turns of thecoils.

As illustrated in FIG. 26, a thrust force of about 140 N is obtained ina range in which the thrust force is proportional to the drive current.Since flat plate magnets magnetized in the axial direction of the moverare not provided, the value of the thrust force is slightly reducedaccordingly as compared with the example of the fourth embodiment (about160 N). However, compared with a phase independent type linear motor ora three-phase drive linear motor, a shorter length is realized, and sizereduction and space saving are achieved.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiments are therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1-11. (canceled)
 12. A mover of a linear motor, which is provided with aplurality of flat plate permanent magnets at outer surfaces of acornered tubular inner yoke made of a soft magnetic material,comprising: a plurality of flat plate magnets magnetized in a directionperpendicular to the outer surface of the inner yoke as the plurality offlat plate permanent magnets; and a plurality of flat plate magnetsmagnetized in an axial direction of the inner yoke as the plurality offlat plate permanent magnets, wherein the flat plate magnets magnetizedin the perpendicular direction and the flat plate magnets magnetized inthe axial direction are alternately and continuously arranged at eachouter surface of the inner yoke along the axial direction of the inneryoke, wherein the flat plate magnets magnetized in the perpendiculardirection comprise first flat plate magnets magnetized from inside ofthe inner yoke to outside thereof and second flat plate magnetsmagnetized from the outside of the inner yoke to the inside thereof, andthe first and second flat plate magnets are alternately arranged alongthe axial direction of the inner yoke, wherein the flat plate magnetsmagnetized in the axial direction are each magnetized from the adjacentsecond flat plate magnet to the adjacent first flat plate magnet, andwherein positions of the plurality of flat plate permanent magnetsprovided at the outer surfaces of the inner yoke are deviated from eachother.
 13. The mover according to claim 12, wherein the positions of theplurality of flat plate permanent magnets provided at the outer surfacesof the inner yoke are deviated from each other in the axial direction bya dimension equal to or less than ¼ of a total length of one of thefirst flat plate magnets, one of the second flat plate magnets and twoof the flat plate magnets magnetized in the axial direction.
 14. Themover according to claim 12, wherein a linear guide rail for supportingthe mover is provided at a corner portion of the outer surface of theinner yoke so as to be extended in the axial direction of the inneryoke.
 15. A mover of a linear motor, which is provided with a pluralityof flat plate permanent magnets at four outer surfaces of a quadrangulartubular inner yoke made of a soft magnetic material, comprising: aplurality of flat plate magnets magnetized in a direction perpendicularto the outer surface of the inner yoke as the plurality of flat platepermanent magnets; and a plurality of flat plate magnets magnetized inan axial direction of the inner yoke as the plurality of flat platepermanent magnets, wherein the flat plate magnets magnetized in theperpendicular direction and the flat plate magnets magnetized in theaxial direction are alternately and continuously arranged at each outersurface of the inner yoke along the axial direction of the inner yoke,wherein the flat plate magnets magnetized in the perpendicular directioncomprise first flat plate magnets magnetized from inside of the inneryoke to outside thereof and second flat plate magnets magnetized fromthe outside of the inner yoke to the inside thereof, and the first andsecond flat plate magnets are alternately arranged along the axialdirection of the inner yoke, wherein the flat plate magnets magnetizedin the axial direction are each magnetized from the adjacent second flatplate magnet to the adjacent first flat plate magnet, and whereinpositions of the plurality of flat plate permanent magnets provided atone pair of the adjacent outer surfaces of the inner yoke and positionsof the plurality of flat plate permanent magnets provided at the otherpair of the adjacent outer surfaces of the inner yoke are deviated fromeach other by ¼ of a total length of one of the first flat platemagnets, one of the second flat plate magnets and two of the flat platemagnets magnetized in the axial direction.
 16. A linear motorcomprising: a mover in which a plurality of flat plate permanent magnetsat outer surfaces of a cornered tubular inner yoke made of a softmagnetic material comprise flat plate magnets magnetized in a directionperpendicular to the outer surface of the inner yoke and flat platemagnets magnetized in an axial direction of the inner yoke, the flatplate magnets magnetized in the perpendicular direction and the flatplate magnets magnetized in the axial direction are alternately andcontinuously arranged at each outer surface of the inner yoke along theaxial direction of the inner yoke, the flat plate magnets magnetized inthe perpendicular direction comprise first flat plate magnets magnetizedfrom inside of the inner yoke to outside thereof and second flat platemagnets magnetized from the outside of the inner yoke to the insidethereof, the first and second flat plate magnets are alternatelyarranged along the axial direction of the inner yoke, the flat platemagnets magnetized in the axial direction are each magnetized from theadjacent second flat plate magnet to the adjacent first flat platemagnet, and positions of the plurality of flat plate permanent magnetsprovided at the outer surfaces of the inner yoke are deviated from eachother; and an armature in which the armature comprises a first singlepole unit made of a soft magnetic material and having a rectangularopening, a yoke portion located outwardly of the opening, and a coreportion extended from the yoke portion to the opening, and a secondsingle pole unit made of a soft magnetic material and having arectangular opening, a yoke portion located outwardly of the opening,and a core portion that is located at a position rotated by 90° from aposition of the core portion of the first single pole unit and that isextended from the yoke portion to the opening, the first and secondsingle pole units are alternately stacked, and windings are wound arounda plurality of the core portions of the first single pole unit and/or aplurality of the core portions of the second single pole unit, whereinthe mover is passed through the opening of the first single pole unitand the opening of the second single pole unit.
 17. The linear motoraccording to claim 16, wherein the inner yoke has a quadrangular tubularshape, the openings each have a quadrangular shape, the first and secondsingle pole units each have a quadrangular shape, and an angle of 45° isformed between a direction of a side of each of the first and secondsingle pole units and a direction of a side of the opening.
 18. Thelinear motor according to claim 16, wherein a spacer made of a softmagnetic material is interposed between the stacked first and secondsingle pole units so that the core portions of the first and secondsingle pole units do not come into contact with each other.
 19. A linearmotor comprising: a mover in which a plurality of flat plate permanentmagnets at outer surfaces of a cornered tubular inner yoke made of asoft magnetic material comprise first flat plate magnets magnetized frominside of the inner yoke to outside thereof and second flat platemagnets magnetized from the outside of the inner yoke to the insidethereof, the first and second flat plate magnets are alternatelyarranged at each outer surface of the inner yoke along the axialdirection of the inner yoke, and positions of the plurality of flatplate permanent magnets provided at the outer surfaces of the inner yokeare deviated from each other; and an armature in which the armaturecomprises a first single pole unit made of a soft magnetic material andhaving a rectangular opening, a yoke portion located outwardly of theopening, and a core portion extended from the yoke portion to theopening, and a second single pole unit made of a soft magnetic materialand having a rectangular opening, a yoke portion located outwardly ofthe opening, and a core portion that is located at a position rotated by90° from a position of the core portion of the first single pole unitand that is extended from the yoke portion to the opening, the first andsecond single pole units are alternately stacked, and windings are woundaround a plurality of the core portions of the first single pole unitand/or a plurality of the core portions of the second single pole unit,wherein the mover is passed through the opening of the first single poleunit and the opening of the second single pole unit.
 20. The linearmotor according to claim 19, wherein the inner yoke has a quadrangulartubular shape, the openings each have a quadrangular shape, the firstand second single pole units each have a quadrangular shape, and anangle of 45° is formed between a direction of a side of each of thefirst and second single pole units and a direction of a side of theopening.
 21. The linear motor according to claim 19, wherein a spacermade of a soft magnetic material is interposed between the stacked firstand second single pole units so that the core portions of the first andsecond single pole units do not come into contact with each other.
 22. Alinear motor comprising: a mover in which a plurality of flat platepermanent magnets at four outer surfaces of a quadrangular tubular inneryoke made of a soft magnetic material comprise flat plate magnetsmagnetized in a direction perpendicular to the outer surface of theinner yoke and flat plate magnets magnetized in an axial direction ofthe inner yoke, the flat plate magnets magnetized in the perpendiculardirection and the flat plate magnets magnetized in the axial directionare alternately and continuously arranged at each outer surface of theinner yoke along the axial direction of the inner yoke, the flat platemagnets magnetized in the perpendicular direction comprise first flatplate magnets magnetized from inside of the inner yoke to outsidethereof and second flat plate magnets magnetized from the outside of theinner yoke to the inside thereof, the first and second flat platemagnets are alternately arranged along the axial direction of the inneryoke, the flat plate magnets magnetized in the axial direction are eachmagnetized from the adjacent second flat plate magnet to the adjacentfirst flat plate magnet, and positions of the plurality of flat platepermanent magnets provided at one pair of the adjacent outer surfaces ofthe inner yoke and positions of the plurality of flat plate permanentmagnets provided at the other pair of the adjacent outer surfaces of theinner yoke are deviated from each other by ¼ of a total length of one ofthe first flat plate magnets, one of the second flat plate magnets andtwo of the flat plate magnets magnetized in the axial direction; and anarmature in which the armature comprises a first single pole unit madeof a soft magnetic material and having a rectangular opening, a yokeportion located outwardly of the opening, and a core portion extendedfrom the yoke portion to the opening, and a second single pole unit madeof a soft magnetic material and having a rectangular opening, a yokeportion located outwardly of the opening, and a core portion that islocated at a position rotated by 90° from a position of the core portionof the first single pole unit and that is extended from the yoke portionto the opening, the first and second single pole units are alternatelystacked, and first and second windings are wound around two areas of aplurality of the core portions of the first single pole unit or aplurality of the core portions of the second single pole unit, whereinthe mover is passed through the opening of the first single pole unitand the opening of the second single pole unit so that the plurality offlat plate permanent magnets at said one pair of the outer surfaces areopposed to the first winding and the plurality of flat plate permanentmagnets at the other pair of the outer surfaces are opposed to thesecond winding, and wherein currents by which a phase difference of anelectrical angle of 90° occurs are applied to the first and secondwindings.
 23. The linear motor according to claim 22, wherein thepositions of the plurality of flat plate permanent magnets provided atsaid one pair of the outer surfaces are deviated from each other, andthe positions of the plurality of flat plate permanent magnets providedat the other pair of the outer surfaces are deviated from each other.24. The linear motor according to claim 22, wherein spacing between thefirst and second single pole units, which are adjacent to each other, isadjusted.
 25. The linear motor according to claim 22, wherein the inneryoke has a quadrangular tubular shape, the openings each have aquadrangular shape, the first and second single pole units each have aquadrangular shape, and an angle of 45° is formed between a direction ofa side of each of the first and second single pole units and a directionof a side of the opening.
 26. The linear motor according to claim 22,wherein a spacer made of a soft magnetic material is interposed betweenthe stacked first and second single pole units so that the core portionsof the first and second single pole units do not come into contact witheach other.